This invention relates to the manufacture of fiber reinforced materials and more particularly to a new and improved process for making elastomeric compounds reinforced with chopped fibers. To improve the physical properties of fiber reinforced elastomers, such as stiffness and modulus, it has become desirable to incorporate filamentary reinforcing materials to the elastomer prior to the molding or shaping into the desired form. One method of fabricating hose and belts utilizes an extruder and has the fiber material injected into the hose by blowing the fibers against the hose. Another method is to extrude a product with an elastomeric compound containing fibers mixed into the compound at the extruder. Other methods include the chopping of fibers to the desired length and then admixing the fibers to the compound and then molding the compound to the desired stage. One problem encountered in the manufacture of fiber loaded compounds is that standard techniques pose problems in the mixing stage as where there is incorporation into the elastomeric compound of fibers greater than 20 parts per 100 parts of elastomer. The problems include difficulty in bagging, handling of the dry mixes, compound splitting and crumbling. Staple fibers are produced in various lengths, depending on their end use, ranging from 1/4 of an inch for specialty papers, up to 5, 6 or 7 inches for blending with wool or other carpet fibers. The most common staple fiber lengths are 11/2-1-9/16 inches intended to match appropriate grades of cotton fibers for use in the cotton spinning system.
The present invention is concerned with the improvement of fiber loaded elastomers or rubbers by introducing within the elastomeric or rubber materials itself filaments of long length such as approximately 1.6 inches in length with a diameter of 11 microns which it has been found in the processing technique used to increase processability and ending up with a product that has the fibers of small length (an average fiber length of approximately 0.125 inches). In the improved process, by starting out with extremely long fibers, it is easier to handle the materials, obtain a better distribution of the fibers and a subsequent breakdown of the fiber lengths to achieve a product with enhanced strength characteristics of the composite. Such increased strength characteristics include the entanglement of the fibers and their orientation which results from such processes. The term rubber as used herein includes rubber and the various synthetic materials having, or which may be compounded to impart, the characteristic flexibility and extensibility of rubber. The term rubber includes neoprene or nitrile rubber compounds. The fiber loaded composites containing the chopped fibers are particularly useful in enhancing the properties of the compound for use in tires, hose, belts and similar products.
The term elastomer is defined as a substance that can be stretched at room temperature to at least twice its original length and, after having been stretched and the stress removed, returns with force to approximately its original length in a short time. (See Glossary of Terms as prepared by ASTM Committee D-11 on Rubber and Rubber-like Materials. Published by the American Society for Testing Materials).
The elastomeric or rubber materials that can be used include natural rubber, copolymers of butadiene and acrylonitrile, copolymers of butadiene and styrene, copolymers of butadiene and alkyl acrylates, butyl rubber, olefin rubbers such as ethylene-propylene and EPDM rubber, flurocarbon rubbers, flurosilicone rubbers, silicone rubbers, chlorosulfonated polyethylene, polyacrylates, polybutadiene, polychloroprene and the like.
Preferred elastomeric materials include natural rubber, copolymers of butadiene/acrylonitrile and copolymers of butadiene and styrene which is often referred to as SBR.
Staple fibers are produced in various lengths, depending on their end use, ranging from 1/4 inch for specialty papers up to 5, 6 or 7 inches for blending with wool or other carpet fibers. The most common staple fiber lengths are 11/2 inch to 1-9/16 inch.